Internal Economy - Game Mechanics: Advanced Game Design - page 61

Note that in video games some resources that might appear to be abstract are in
fact quite concrete. For example, experience points are not an abstract resource in a
role-playing game. Instead, they are an intangible, but real, commodity that must
be earned and (sometimes) spent like money. Happiness and reputation are two more
resources used by many games that, although they are intangible, are nevertheless
concrete parts of the game.
To design a game's internal economy or to study the internal economy of an exist-
ing game, it is most useful to start identifying the main resources and only then
describe the mechanisms that govern the relationships between them and how they
are produced or consumed.
entities
Specific quantities of a resource are stored in entities. (If you are a programmer, an
entity is essentially a variable.) A resource is a general concept, but an entity stores
a specific amount of a resource. An entity named “Timer,” for example, stores the
resource time —probably the number of seconds remaining before the end of the
game. In Monopoly, each player has an entity that stores available cash resources.
As the player buys and sells, pays rent and fines, and so on, the amount of cash in
the entity changes. When a player pays rent to another player, cash flows from the
first player's entity to the second player's entity.
Entities that store one value are called simple entities. Compound entities are groups
of related simple entities, so a compound entity can contain more than one value.
For example, a unit in a strategy game normally includes many simple entities that
describe its health, damage capability, maximum speed, and so on. Collectively,
these make up a compound entity, and the simple entities that make it up are known
as its attributes. Thus, a unit's health is an attribute of the unit.
Four economic Functions
Economies commonly include four functions that affect resources and move them
around. These are mechanics called sources, drains, converters, and traders. We describe
them here. Again, this is a summary; for further details, see Chapter 10 of Fundamentals
of Game Design .
n Sources are mechanics that create new resources out of nothing. At a certain
time, or upon certain conditions, a source will generate a new resource and store it
in an entity somewhere. Sources may be triggered by events in the game, or they
may operate continuously, producing resources at a certain production rate. They
may also be switched on and off. In simulation games, money is often generated
by a source at intervals, with the amount of money created proportional to the
population. As another example, some games that involve combat automatically
regenerate health over time.